2024-16166. Marine Mammals; Incidental Take During Specified Activities; Proposed Incidental Harassment Authorization for Southcentral Alaska Stock of Northern Sea Otters in Whittier, AK; Draft Environmental Assessment

Table 1—Temporary Threshold Shift (TTS) and Permanent Threshold Shift (PTS) Thresholds Established by Southall et al. (2019) Through Modeling and Extrapolation for “Other Marine Carnivores,” Which Include Sea Otters *

	TTS			PTS
	nonimpulsive	impulsive		nonimpulsive	impulsive
	SEL CUM	SEL CUM	Peak SPL	SEL CUM	SEL CUM	Peak SPL
Air	157	146	170	177	161	176
Water	199	188	226	219	203	232
* Values are weighted for other marine carnivores' hearing thresholds and given in cumulative sound exposure level (SEL CUM dB re 20 micropascal (μPa) in air and SEL CUM dB re 1 μPa in water) for impulsive and nonimpulsive sounds, and unweighted peak sound pressure level (SPL) in air (dB re 20μPa) and water (dB 1μPa) (impulsive sounds only).

Evidence From Sea Otter Studies

Individual sea otters in Passage Canal will likely show a range of responses to noise from pile-driving activities. Some sea otters will likely dive, show startle responses, change direction of travel, or prematurely surface. Sea otters reacting to pile-driving activities may divert time and attention from biologically important behaviors, such as feeding and nursing pups. Sea otter responses to disturbance can result in energetic costs, which increases the amount of prey required by sea otters (Barrett 2019). This increased prey consumption may impact sea otter prey availability and cause sea otters to spend more time foraging and less time resting (Barrett 2019). Some sea otters may abandon the project area and return when the disturbance has ceased. Based on the observed movement patterns of sea otters (Lensink 1962; Kenyon 1969, 1981; Garshelis and Garshelis 1984; Riedman and Estes 1990; Tinker and Estes 1996), we expect some individuals will respond to pile-driving activities by dispersing to nearby areas of suitable habitat; however other sea otters, especially territorial adult males, will not be displaced.

Additional information on the evidence from studies about how sea otters may be affected by sound can be found in the supplemental information to this document (available as described above in ADDRESSES ).

Consequences of Disturbance

Information on the consequences of disturbance to sea otters can be found in the supplemental information to this document (available as described above in ADDRESSES ).

Vessel Activities

Vessel activity during the project includes the transit of three barges for materials and construction, all of which will remain on site, mostly stationary, to support the work; additionally, two skiffs will be used during the project: one for transporting workers short distances to the crane barge and the other for marine mammal monitoring during pile driving. Vessels will not be used extensively or over a long duration during the planned work; therefore, we do not anticipate that sea otters will experience changes in behavior indicative of tolerance or habituation.

Additional information on vessel activities can be found in the supplemental information to this document (available as described above in ADDRESSES ).

Effects on Sea Otter Habitat and Prey

Information on the potential impacts of the specified activities on sea otter prey species can be found in the supplemental information to this document (available as described above in ADDRESSES ).

Potential Impacts of the Specified Activities on Subsistence Uses

The planned specified activities will occur near marine subsistence harvest areas used by Alaska Native peoples from Whittier and the surrounding areas. The majority of sea otter harvest in this area occurs more than 3.2 kilometers (km) (2 miles [mi]) outside of Whittier. Since 2012, there have been 75 sea otters harvested in the Whittier area, and most of those were taken prior to 2017. From 2018 through 2021, only eight sea otters were harvested from the Whittier area.

The planned project would occur within the Whittier city limits, where firearm use is prohibited. The area potentially affected by the planned project does not significantly overlap with current subsistence harvest areas. Construction activities will not preclude access to hunting areas or interfere in any way with individuals wishing to hunt. Despite no conflict with subsistence use being anticipated, the FWS will conduct outreach with potentially affected communities to see whether there are any questions, concerns, or potential conflicts regarding subsistence use in those areas. If any conflicts are identified in the future, TMC will develop a plan of cooperation specifying the steps necessary to minimize any effects the project may have on subsistence harvest.

Estimated Take

Definitions of Incidental Take Under the Marine Mammal Protection Act

Below we provide definitions of potential types of take of northern sea otters. The FWS does not anticipate and is not proposing to authorize lethal take as a part of this proposed IHA, nor did the applicant request authorization of lethal take; however, the definitions of these take types are provided for context and background.

Lethal Take— Human activity may result in biologically significant impacts to northern sea otters. In the most serious interactions, human actions can result in the mortality of sea otters.

Level A Harassment— Human activity may result in the injury of sea otters. Level A harassment for nonmilitary readiness activities is defined as any act of pursuit, torment, or annoyance that has the potential to injure a marine mammal or marine mammal stock in the wild.

Level B Harassment— Level B harassment for nonmilitary readiness activities means any act of pursuit, torment, or annoyance that has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behaviors or activities, including, but not limited to, migration, breathing, nursing, feeding, or sheltering. Human-caused changes in behavior that disrupt biologically significant behaviors or activities for the affected animal indicate take by Level B harassment under the MMPA.

The FWS has identified the following sea otter behaviors as indicative of possible Level B harassment:

• Swimming away at a fast pace on belly (i.e., porpoising);
• Repeatedly raising the head vertically above the water to get a better view (spyhopping) while apparently agitated or while swimming away;
• In the case of a pup, repeatedly spyhopping while hiding behind and holding onto its mother's head;
• Abandoning prey or feeding area;
• Ceasing to nurse and/or rest (applies to dependent pups);
• Ceasing to rest (applies to independent animals);
• Ceasing to use movement corridors;
• Ceasing mating behaviors;
• Shifting/jostling/agitation in a raft so that the raft disperses;
• Sudden diving of an entire raft; or
• Flushing animals off a haulout.

This list is not meant to encompass all possible behaviors; other behavioral responses may also be indicative of Level B harassment. Relatively minor changes in behavior such as increased vigilance or a short-term change in direction of travel are not likely to disrupt biologically important behavioral patterns, and the FWS does not view such minor changes in behavior as indicative of Level B harassment.

Calculating Take

We assumed all animals exposed to underwater sound levels that meet the acoustic exposure criteria defined above in Exposure Thresholds will experience take by Level A harassment or Level B harassment due to exposure to underwater noise. Spatially explicit zones of ensonification were established around the planned construction location to estimate the number of otters that may be exposed to these sound levels. We determined the number of otters present in the ensonification zones using density information generated by Esslinger et al. (2021).

The project can be divided into four major components: DTH drilling, vibratory drilling, pile driving using an impact driver, and skiff use to support construction. Each of these components will generate a different type of in-water noise. Vibratory drilling and the use of skiffs will produce nonimpulsive or continuous noise; impact driving will produce impulsive noise; and DTH drilling is considered to produce both impulsive and continuous noise (NMFS 2020).

The level of sound anticipated from each project component was established using recorded data from several sources listed in tables 2 through 5. We used the empirical data from those proxy projects with the NMFS Technical Guidance and User Spreadsheet (NMFS 2018, 2020) to determine the distance at which sound levels would attenuate to Level A harassment thresholds (table 1). To estimate the distances at which sounds would attenuate to Level B harassment thresholds (table 1), we used the data from the proxy projects with the NMFS-recommended transmission loss coefficient of 15 for coastal pile-driving activities in a practical spreading loss model (NMFS 2020) to determine the distance at which sound levels attenuate to 160 dB re 1 μPa. The weighting factor adjustment included in the NMFS user spreadsheet accounts for sounds created in portions of an organism's hearing range where they have less sensitivity. We used the weighting factor adjustment for otariid pinnipeds as they are the closest available physiological and anatomical proxy for sea otters. The spreadsheet also incorporates a transmission loss coefficient, which accounts for the reduction in sound level outward from a sound source. We used the NMFS-recommended transmission loss coefficient of 15 for coastal pile-driving activities to indicate practical spread (NMFS 2020).

We calculated the harassment zones for DTH drilling with input from NMFS. The SPLs produced by DTH drilling were provided by NMFS in 2022 via correspondence with Solstice Alaska Consulting, who created the application for this IHA on behalf of TMC, as well as from the NMFS proposed IHA for this project in 2023. We then used the provided SPLs with the NMFS Technical Guidance and User Spreadsheet (NMFS 2018, 2020) to determine the distance at which these sounds would attenuate to Level A harassment thresholds. To estimate the distances at which sounds would attenuate to Level B harassment thresholds, we used the provided SPLs with a NMFS-recommended transmission loss coefficient of 15 for coastal pile-driving activities in a practical spreading loss model (NMFS 2020) to determine the distance at which sound levels attenuate to 160 dB re 1 μPa. To ensure the most conservative harassment thresholds, peak SPL of 194 dB re 1 μPa (Heyvaert and Reyff 2021) was included in the calculations of Level B harassment thresholds for DTH pile driving. However, due to the differences in how PTS and TTS thresholds are calculated, as well as limited data of underwater SPLs from DTH drilling, the resultant Level A isopleths for DTH installation of 122-cm (48-in) steel piles are larger than the Level B isopleths.

Table 2—Summary of Sound Level, Timing of Sound Production, Distance From Sound Source to Below Level A Harassment and Level B Harassment Thresholds, Days of Impact, Sea Otters in Level A and Level B Harassment Ensonification Area, and Total Otters Expected To Be Harassed Through Behavioral Disturbance by Vibratory Drilling

Pile size	91-cm (36-in) (temporary)- installation	91-cm (36-in) (temporary)- removal	91-cm (36-in) (permanent)	122-cm (48-in) (permanent)
Total number of piles	15	15	7	8.
Sound level	166 dB re 1μPa at 10 m (RMS)			168.2 dB re 1μPa at 10 m (RMS).
Source	NAVFAC a 2015			Austin et al. 2016.
Timing per pile	10 minutes/pile	10 minutes/pile	15 minutes/pile	15 minutes/pile.
Maximum number of piles per day	4	4	4	2.
Maximum number of days of activity	4	4	2	4.
Sea otter density	2.03 sea otters/km2
Distance to below Level A harassment threshold	0.5 meters	0.5 meters	0.6 meters	0.6 meters.
Level A area (km2 )	0.000001	0.000001	0.000001	0.000001.
Potential sea otters affected by Level A sound per day	0.000002	0.000002	0.000002	0.000002.
Potential sea otters affected by Level A sound per day (rounded)	0	0	0	0.
Total potential Level A harassment events	0	0	0	0.
Distance to below Level B harassment threshold	25 meters	25 meters	25 meters	35 meters.
Level B area (km2 )	0.002	0.0020	0.0020	0.0038.
Potential sea otters affected by Level B sound per day	0.0040	0.0040	0.004	0.0078.
Potential sea otters affected by Level B sound per day (rounded)	0	0	0	0.
Total potential Level B harassment events	0	0	0	0.
a  Naval Facilities Engineering Command.

Table 3—Summary of Sound Level, Timing of Sound Production, Distance From Sound Source to Below Level A Harassment and Level B Harassment Thresholds, Days of iMpact, Sea Otters in Level A and Level B Harassment Ensonification Area, and Total Otters Expected To Be Harassed Through Behavioral Disturbance by Impact Pile Driving

Pile size	91-cm (36-in) (permanent)	122-cm (48-in) (permanent)
Total number of piles	7	8.
Sound level	184 dB (SEL)/192 dB (RMS)/211 dB (peak) re 1μPa at 10 m	186.7 dB (SEL)/198.6 dB (RMS)/212 dB (peak) re 1μPa at 10 m.
Source	NAVFAC 2015	Austin et al. 2016.
Timing per pile	45 minutes/pile; 1,800 strikes/pile	60 minutes/pile; 2,400 strikes/pile.
Maximum number piles per day	4	2.
Maximum number of days of activity	2	4.
Sea otter density	2.03 sea otters/km2 .
Distance to below Level A harassment threshold	169.2 meters	195.4 meters.
Level A area (km2 )	0.0718	0.1199.
Potential sea otters affected by Level A sound per day	0.1458	0.2435.
Potential sea otters affected by Level A sound per day (rounded)	1	1.
Total potential Level A harassment events	2	4.
Distance to below Level B harassment threshold	1,359 meters	3,744 meters.
Level B area (km2 )	1.9161	7.8846.
Potential sea otters affected by Level B sound per day	3.8897	16.0058
Potential sea otters affected by Level B sound per day (rounded)	4	16.
Total potential Level B harassment events	8	64.

Table 4—Summary of Sound Level, Timing of Sound Production, Distance From Sound Source to Below Level A Harassment and Level B Harassment Thresholds, Days of Impact, Sea Otters in Level A and Level B Harassment Ensonification Area, and Total Otters Expected To Be Harassed Through Behavioral Disturbance by Down-the-Hole Drilling

Pile size	91-cm (36-in) (temporary)	91-cm (36-in) (permanent)	122-cm (48-in) (permanent)
Total number of piles	10 (installation only)	7	8.
Sound level	164 dB (SEL)/174 dB (RMS)/194 (peak) re 1μPa at 10 m.		171 dB (SEL)/174 (RMS)/194 (peak) dB re 1μPa at 10 m.
Source	Reyff and Heyvaert 2019; Reyff 2020; Denes et al. 2019; Heyvaert and Reyff 2021; NMFS 2023.		SolsticeAK 2022; Heyvaert and Reyff 2021; NMFS 2023.
Timing per pile	60 minutes/pile	150 minutes/pile	150 minutes/pile.
Maximum number piles per day	4	2	2.
Maximum number of days of activity	3	4	4.
Sea otter density	2.03 sea otters/km2 .
Distance to below Level A harassment threshold	57.9 meters	67.1 meters	196.6 meters.a
Level A area (km2 )	0.0105	0.0141	0.1214.
Potential sea otters affected by Level A sound per day	0.0214	0.0287	0.2465.
Potential sea otters affected by Level A sound per day (rounded)	1	1	1.
Total potential Level A harassment events	3	4	4.
Distance to below Level B harassment threshold	85.8 meters	85.8 meters	85.8 meters.a
Level B area (km2 )	0.0231	0.0231	0.0231.
Potential sea otters affected by Level B sound per day	0.0469	0.0469	0.0469.
Potential sea otters affected by Level B sound per day (rounded)	1	1	1.
Total potential Level B harassment events	3	4	4.
a  Due to differences in how PTS and TTS thresholds are calculated, the Level A isopleths are larger than the Level B isopleths.

Table 5—Summary of Sound Level, Timing of Sound Production, Distance From Sound Source to Below Level A Harassment and Level B Harassment Thresholds, Days of Impact, Sea Otters in Level A and Level B Harassment Ensonification Area, and Total Otters Expected To Be Harassed Through Behavioral Disturbance by Use of Skiffs

Sound source	Monitoring skiff	Worker transit skiff
Sound level	175 dB (RMS) re 1μPa at 1 m	175 dB (RMS) re 1μPa at 1 m.
Source	Richardson et al. 1995; Kipple and Gabriele 2007.
Number of days of vessel use	31	31.
Sea otter density	2.03 sea otters/km2 .
Distance to below Level A harassment threshold	0 meters	0 meters.
Level A area (km2 )	0	0.
Potential sea otters affected by Level A sound per day	0	0.
Potential sea otters affected by Level A sound per day (rounded)	0	0.
Total potential Level A harassment events	0	0.
Distance to below Level B harassment threshold	10 meters	10 meters.
Level B area (km2 )	0.2832	0.0095.
Potential sea otters affected by Level B sound per day	0.5748	0.0192.
Potential sea otters affected by Level B sound per day (rounded)	1	1.
Total potential Level B harassment events	31	31.

Sound levels for all sources are unweighted and given in dB re 1 μPa. Nonimpulsive sounds are in the form of mean maximum root mean square (RMS) SPL as it is more conservative than SEL_CUM or peak SPL for these activities. Impulsive sound sources are in the form of SEL for a single strike.

To determine the number of sea otters that may experience in-water sounds >160 dB re 1μPa due to pile driving, we multiplied the area ensonified to >160 dB re 1μPa by the density of animals (2.03 sea otters per square kilometer (km² )) derived from surveys conducted of Prince William Sound (Esslinger et al. 2021). We applied the same methodology to determine the number of sea otters that may experience sounds capable of causing PTS. The number of sea otters expected to be exposed to such sound levels can be found in tables 2 through 5. To calculate the area ensonified for each type of pile-driving activity, the coordinates of the piles were mapped in ArcGIS Pro. We used a representative pile of each size around which to map the Level A harassment and Level B harassment zones. We chose representative piles that were farthest from shore so that the zones that are intercepted by land have the largest in-water areas possible. The majority of these radii are small enough that their defined circles will fall entirely in the water, and in these instances, the area was calculated as πr² . The exceptions are the Level A and Level B zones generated by impact pile driving the 91-cm (36-in) permanent piles as well as the Level B zone generated by impact pile driving the 122-cm (48-in) piles; for these, we used ArcGIS Pro to map and calculate the area of the water ensonified by those activities.

The area ensonified by the worker transit skiff was estimated by multiplying the vessel's anticipated daily track length by twice the 160 dB radius plus πr² to account for the rounded ends of the track line. It was estimated that the distance of each trip would be no more than 457.2 m (1,500 ft). The worker transit skiff transports crew between shore and the work platform. It will be in use the same days that pile driving occurs but is not expected to be used while piles are being driven.

The monitoring skiff will travel in a triangle of perimeter approximately 7 km (4.3 mi) between Emerald Island, the north shore of Passage Canal, and Gradual Point during pile driving activities, but outside the largest Level B harassment threshold. To estimate the area ensonified by the monitoring skiff, we used ArcGIS Pro to plot the points of the triangle, map the track line between those points, and apply a buffer of 10 m (33 ft; the 160-dB radius) on either side of the track line.

We assumed that the different types of pile-driving activities would occur sequentially and that the total number of days of work would equal the sum of the number of days required to complete each type of pile-driving activity. While it is possible that on some days more than one type of activity will take place, which would reduce the number of days of exposure within a year, we cannot know this information in advance. As such, the estimated number of days and, therefore, exposures per year is the maximum possible for the planned work. Where the number of exposures expected per day was zero to three or more decimal places ( i.e., <0.00X), the number of exposures per day was assumed to be zero.

In order to minimize exposure of sea otters to sounds above Level A harassment thresholds, TMC will implement shutdown zones ranging from 10 to 200 m (33 to 656 ft), based on the pile size and type of pile driving or marine construction activity, where operations will cease should a sea otter enter or approach the specified zone. Soft-start and zone clearance prior to startup will also limit the exposure of sea otters to sound levels that could cause PTS. However, TMC has requested, and the FWS proposes to authorize, small numbers of take by Level A harassment during impact pile driving and DTH drilling.

Although sea otters are non-migratory, they typically move amongst focal areas within their home ranges to rest and forage (Garshelis and Garshelis 1984; Laidre et al. 2009). It is possible that, given the large variability in individual home range sizes and the potential for up to daily movement in and out of foraging or resting areas, different individual sea otters could be found within the ensonification zone each day of the project. Thus, the FWS conservatively assumes that the 162 estimated harassment events may impact up to 162 different sea otters.

Critical Assumptions

We estimate that 145 takes of 145 sea otters by Level B harassment and 17 takes of 17 sea otters by Level A harassment may occur due to TMC's planned cruise ship dock construction activities. In order to conduct this analysis and estimate the potential amount of take by harassment, several critical assumptions were made.

Level B harassment is equated herein with behavioral responses that indicate harassment or disturbance. There is likely a portion of animals that respond in ways that indicate some level of disturbance but do not experience biologically significant consequences.

We used the sea otter density for the Whittier area from surveys and analyses conducted by Esslinger et al. (2021). Methods and assumptions for these surveys can be found in the original publication.

We used sound source verification from recent pile-driving activities in a number of locations within and beyond Alaska to generate sound level estimates for construction activities. Environmental conditions in these locations, including water depth, substrate, and ambient sound levels are similar to those in the project location, but not identical. Further, estimation of ensonification zones were based on sound attenuation models using a practical spreading loss model. These factors may lead to actual sound values differing slightly from those estimated here.

Finally, the pile-driving activities described here will also create in-air noise. Because sea otters spend over half of their day with their heads above water (Esslinger et al. 2014), they will be exposed to an increase in-air noise from construction equipment. However, we have calculated Level B harassment with the assumption that an individual may be harassed only one time per 24- hour period, and underwater sound levels will be more disturbing and extend farther than in-air noise. Thus, while sea otters may be disturbed by noise both in-air and underwater, we have relied on the more conservative underwater estimates.

Sum of Harassment From All Sources

The applicant plans to conduct pile driving and marine construction activities in Whittier, Alaska, over the course of a year from the date of issuance of the IHA. A summary of total estimated take during the project by source is provided in table 6.

Table 6—Total Estimated Takes by Source of Level A Harassment and Level B Harassment of Sea Otters

Source	Number of days of activity	Sea otters exposed per day to Level A harassment	Total takes of sea otters by Level A harassment	Sea otters exposed per day to Level B harassment	Total takes of sea otters by Level B harassment
Vibratory drilling:
91-cm (36-in) (temporary)—installation	4	0	0	0	0
91-cm (36-in) (temporary)—removal	4	0	0	0	0
91-cm (36-in) (permanent)	2	0	0	0	0
122-cm (48-in) (permanent)	4	0	0	0	0
Impact drilling:
91-cm (36-in) (permanent)	2	1	2	4	8
122-cm (48-in) (permanent)	4	1	4	16	64
Down-the-hole drilling:
91-cm (36-in) (temporary)—installation	3	1	3	1	3
91-cm (36-in) (permanent)	4	1	4	1	4
122-cm (48-in) (permanent)	4	1	4	1	4
Skiff use:
Monitoring skiff	31	0	0	1	31
Worker transit skiff	31	0	0	1	31
Totals	93	5	17	25	145

Over the course of the project, we estimate 145 instances of take by Level B harassment of northern sea otters from the Southcentral Alaska stock due to behavioral responses and/or TTS associated with noise exposure. Although multiple instances of Level B harassment of individual sea otters are possible, these events are unlikely to have significant consequences for the health, reproduction, or survival of affected animals and therefore would not rise to the level of an injury or Level A harassment.

The use of soft-start procedures, zone clearance prior to startup, and shutdown zones is likely to decrease both the number of sea otters exposed to sounds above Level A harassment thresholds and the exposure time of any sea otters venturing into a Level A harassment zone. This reduces the likelihood of losses of hearing sensitivity that might impact the health, reproduction, or survival of affected animals. Despite the implementation of mitigation measures, it is anticipated that some sea otters will experience Level A harassment via exposure to underwater sounds above threshold criteria during impact and DTH pile-driving activities. Due to sea otters' small body size and low profile in the water, as well as the relatively large size of the Level A harassment zone associated with these activities, we anticipate that sea otters will at times avoid detection before entering Level A harassment zones for those activities. We anticipate that protected species observers (PSO) will be able to reliably detect and prevent take by Level A harassment of sea otters up to 10 m away; conversely, we anticipate that at distances greater than 10 m, sea otters will at times avoid detection. Throughout the project, we estimate 17 instances of take by Level A harassment of sea otters.

Determinations and Findings

Sea otters exposed to sound from the specified activities are likely to respond with temporary behavioral modification or displacement. The specified activities could temporarily interrupt the feeding, resting, and movement of sea otters. Because activities will occur during a limited amount of time and in a localized region, the impacts associated with the project are likewise temporary and localized. The anticipated effects are short-term behavioral reactions and displacement of sea otters near active operations.

Sea otters that encounter the specified activity may exert more energy than they would otherwise, due to temporary cessation of feeding, increased vigilance, and retreating from the project area. We expect that affected sea otters will tolerate this exertion without measurable effects on health or reproduction. Most of the anticipated takes will be due to short-term Level B harassment in the form of TTS, startling reactions, or temporary displacement. While mitigation measures incorporated into TMC's request will reduce occurrences of Level A harassment to the extent practicable, a small number of take by Level A harassment would be authorized for impact and DTH pile-driving activities, which have Level A harassment zone radii ranging in size from 57.9 to 196.6 m (190 to 645 ft).

With the adoption of the mitigation measures incorporated in TMC's request and required by this proposed IHA, anticipated take was reduced. Those mitigation measures are further described below.

Small Numbers

To assess whether the authorized incidental taking would be limited to “small numbers” of marine mammals, the FWS uses a proportional approach that considers whether the estimated number of marine mammals to be subjected to incidental take is small relative to the population size of the species or stock. Here, predicted levels of take were determined based on the estimated density of sea otters in the project area and ensonification zones developed using empirical evidence from similar geographic areas.

We estimate that TMC's specified activities in the specified geographic region will take no more than 145 takes of 145 sea otters by Level B harassment and 17 takes of 17 sea otters by Level A harassment during the 1-year period of this proposed IHA (see Sum of Harassment from All Sources). Take of 162 animals is 0.7 percent of the best available estimate of the current Southcentral Alaska stock size of 21,617 animals (Esslinger et al. 2021) ((162÷21,617)×100≉0.7) and represents a “small number” of sea otters of that stock.

Negligible Impact

We propose a finding that any incidental take by harassment resulting from the specified activities cannot be reasonably expected to, and is not reasonably likely to, adversely affect the sea otter through effects on annual rates of recruitment or survival and will, therefore, have no more than a negligible impact on the Southcentral Alaska stock of northern sea otters. In making this finding, we considered the best available scientific information, including the biological and behavioral characteristics of the species, the most recent information on species distribution and abundance within the area of the specified activities, the current and expected future status of the stock (including existing and foreseeable human and natural stressors), the potential sources of disturbance caused by the project, and the potential responses of marine mammals to this disturbance. In addition, we reviewed applicant-provided materials, information in our files and datasets, published reference materials, and species experts.

Sea otters are likely to respond to planned activities with temporary behavioral modification or temporary displacement. These reactions are not anticipated to have consequences for the long-term health, reproduction, or survival of affected animals. Most animals will respond to disturbance by moving away from the source, which may cause temporary interruption of foraging, resting, or other natural behaviors. Affected animals are expected to resume normal behaviors soon after exposure with no lasting consequences. Sea otters may move in and out of the project area during pile driving activities, leading to as many as 162 individuals experiencing one day of exposure. However, it is possible that an individual may enter the ensonification area more than once during the project. At most, if the same sea otter enters the ensonification area every day that pile driving occurs, the sea otter would be exposed to pile driving and marine construction noise for up to 31 days. However, injuries ( i.e., Level A harassment or PTS) due to chronic sound exposure are estimated to occur at a longer time scale (Southall et al. 2019). The area that will experience noise greater than Level B thresholds due to pile driving is small (less than 0.13 km² ), and an animal that may be disturbed could escape the noise by moving to nearby quiet areas. Further, sea otters spend over half of their time above the surface during the summer months (Esslinger et al. 2014), and likely no more than 70 percent of their time foraging during winter months (Gelatt et al. 2002); thus, their ears will not be exposed to continuous noise, and the amount of time it may take for permanent injury is considerably longer than that of mammals primarily under water. Some animals may exhibit some of the stronger responses typical of Level B harassment, such as fleeing, interruption of feeding, or flushing from a haulout. These responses could have temporary biological impacts for affected individuals but are not anticipated to result in measurable changes in survival or reproduction.

The total number of animals affected, and severity of impact is not sufficient to change the current population dynamics at the stock scale. Although the specified activities may result in approximately 162 incidental takes of up to 162 sea otters from the Southcentral Alaska stock, we do not expect this level of harassment to affect annual rates of recruitment or survival or result in adverse effects on the stock.

Currently, the best available scientific information indicates that the density of sea otters in the project area is 2.03 sea otters/km² (Esslinger et al. 2021). However, during similar marine construction and pile-driving activities in Whittier under an existing IHA, PSOs collected data which indicate that the proposed project activities may be less impactful than estimated (table 7). No recorded takes by Level A harassment occurred during similar work in Whittier between May 2023 and February 2024, and only 5 takes by Level B harassment occurred over those 10 months.

Table 7—Total Numbers of Observations, Individuals, and Takes by Level A Harassment and Level B Harassment of Sea Otters Under the Initial IHA

Year	Month	Number of sightings	Number of individual sea otters	Number of takes by Level A harassment	Number of takes by Level B harassment
2023	May	1	6	0	0
	June	1	1	0	0
	July	1	1	0	0
	August	5	5	0	0
	September	13	13	0	3
	October	18	22	0	2
	November	7	11	0	0
	December	9	15	0	0
2024	January	6	3	0	0
	February	1	1	0	0
Total		62	78	0	5